The present invention relates to an apparatus for holding motor brushes in an electric motor, and more particularly to an insulator/mounting ring for an electric motor that is especially adaptable for use in industrial electric motors.
Today the electric motor is the method of choice to supply mechanical/electrical energy within industrial environments. As with any other electromechanical device, electric motors require periodic maintenance to ensure that they are working properly and at the highest efficiency level possible. One area that requires periodic maintenance is the carbon brushes in the motor. These brushes need to be replaced periodically in order to provide the maximum transfer of electric current between the stator and armature of the motor.
The user""s ability to replace the carbon brushes is largely dependent upon the environment in which the motor resides. Some environments permit easy maintenance access to a motor and its brushes, thereby making replacement of the brushes quite easy and quick. However, other environments provide very restricted access to the motor and its brushes. These restricted access environments include those associated with large electric motors such as those found in motors that power heavy industrial machinery and those that power diesel-electric locomotives. In such restricted maintenance access environments, the replacement of the motor""s brushes can be an extremely time consuming process, often requiring the removal of the motor""s housing and insulator ring/brushholder mounting ring.
Typically, the electric motors for which the present invention will be most useful contain four or more carbon brushes equally spaced around the commutator of the motor. Usually, the brushes are disposed around the exterior of the cylindrical commutator and are separated by 90xc2x0, with a brush being disposed above, below and on each side of the motor. On some motors, the brushes are disposed at about 0xc2x0, 30xc2x0, 180xc2x0, and 240xc2x0 from top dead center (TDC). The brushes are accessible through an access door located on the side of the motor housing. However, most such access doors allow access to only those two brushes that are mounted on the same side of the commutator as the access door (e.g. at 30xc2x0 and 240xc2x0 from TDC) and do not allow access to the other two brushes (e.g. those at 0xc2x0 and 180xc2x0). This makes it very difficult, if not impossible to change all four brushes in an electric motor without completely disassembling the motor, and removing all or part of it from the housing.
Additionally, the brushes should not be positioned exactly vertically or horizontally around the armature. Typically, the brushes are rotated approximately three degrees from vertical or horizontal. For example the brush mounted to the top of the motor is not centered on the axis of the motor, but rather is rotated three degrees from vertical about the axis of the motor. Nonetheless, the brushes should maintain the critical ninety degree offset from each other.
The difficulty in replacing the brushes results in two undesirable effects. First, motors are not maintained as often as they should be, thereby reducing their efficiency and increasing electricity costs. Second, when a motor is to be repaired, it is typically removed from the environment to which it is operating and replaced by another motor. This requires the factory or industrial facility to maintain a supply of spare motors which therefore increases both labor expense and capital costs. The factory must pay the labor costs to switch out the two motors, transportation costs to move the motor to a repair specialist, as well as the labor costs to have a motor repair specialist disassemble the old motor, replace the brushes and re-assemble the motor. This process typically costs the factory $500.00 to $1,000.00 in extra labor, excessive downtime on the production line due to the added time required to switch out the motors, and the additional costs to maintain a supply of spare motors.
Another problem with current brush mounting systems is that their mounting bolt arrangements add to the difficulty of replacing the brushes. Current brush mounting systems have a ring made of thermo-setting plastic that is secured to the motor housing. The ring typically has four platforms that extend axially outwardly to provide a seat to attach the brush holders. These platforms have a pair of axially extending apertures through which bolts can pass. These apertures are typically longer than the length of the bolt that passes through them. Because of this, the bolts sometimes recede back into this ring when the brush brackets are removed or installed. If this happens, the factory or industrial facility is often forced to completely disassemble the motor again. This process of retrieving the receded bolts adds both additional time as well as frustration to the motor repair specialist during the brush charging process.
In accordance with the present invention, an apparatus is provided for positioning at least one motor brush in an electric motor having a motor housing. The apparatus comprises a base ring secured to the motor housing; an upper ring disposed adjacent to and moveable relative to the base ring; and a mounting member movable between a fixed position and a released position. The mounting member, when in the fixed position is engagable with the upper ring and the base ring to prevent the relative movement of the upper ring and the base ring. When in the released position, the mounting member releases the engagement between the upper ring and the base ring to permit the relative motion of the upper ring and the base ring.
Preferably, the apparatus comprises a two piece, rotatable insulator for holding motor brushes. The insulator is preferably composed of an electrically insulating material such as machinable phonetic, machinable epoxies, polyesters, or other types of insulation material. The insulator includes a lower or base ring and an upper ring. The base ring is secured to the housing in which the motor is placed with two or more bolts, and is fixed in its position with respect to the motor housing. The base ring has a radially inwardly facing surface; three axially facing surfaces, and two radially outwardly facing surfaces of different diameters with the larger diameter surface location positioned for being disposed next to the motor housing. The reduced diameter radially outwardly facing surface provides a centering collar for the upper ring.
The outwardly facing outer surface of the base ring is used as mounting lip for positioning and connecting the lower ring to the housing via a bolt and washer combination.
The main portion of the upper ring comprises a ring having three axially facing surfaces and three radially facing surfaces. A radially outwardly facing surface is concentric with, and has a smaller diameter than the larger diameter radially outwardly facing surface of the base ring. The diameter is smaller so that the radially outwardly facing surface of the upper ring will be disposed radially inwardly from the radially outwardly facing surface of the base ring, thereby permitting the mounting bolts to clear the upper ring, and permit the upper ring to position itself flush against the base ring.
The two radially inwardly facing surfaces of the upper ring have different diameters. The larger diameter, radially inwardly facing surface is concentric with, and approximately the same diameter as the reduced diameter, radially outwardly facing surface of the base ring which is defined as the collar. The diameters of these two surfaces differ enough to allow for a slip fit assembly of the two components and the rotation of the upper ring relative to the base ring, but are close enough to maintain some frictional contact between themselves. The smaller diameter, axially inwardly facing surface of the upper ring in conjunction with the larger diameter, axially outwardly facing surface of the base ring provide a stop axial surface for the axially outwardly facing surface of the base ring.
The smaller, radially inwardly facing cylindrical interior surfaces of the upper ring and lower ring preferably have identical diameters that are large enough to provide sufficient clearance within the diameter of the smaller radially inwardly facing interior surfaces to provide clearance for other components of the motor. In addition to the ring portion, the upper ring has four platforms extending axially outwardly from the axially outwardly facing top surface of the ring. These platforms each have two axially extending apertures to accept bolts for securing the motor brush holder to the axially outer end of the platforms. The apertures have a reduced diameter portion through which the tail end of the bolt passes and a relatively enlarged diameter portion for receiving the head of the bolt. The enlarged diameter portion of the aperture is not cylindrical in its configuration. Rather, it should be slotted, ovaloid or hexagonal in cross section and approximately the size of the head of the bolt to provide at least two opposed flat surfaces to grip the flat sides of the bolt to impede rotational movement of the bolt.
The upper ring includes one or more axially extending indexing mounting bolt receiving apertures that extend entirely through the upper ring, and are alignable with one or more threaded axially extending indexing bolt receiving apertures that extend through the axially outwardly facing surface of the base ring, and partially through the base ring, thus holding the base and upper ring together. However, the indexing bolt receiving aperture of the base ring does not extend all the way to the axially inwardly facing surface of the base ring which is flush against the motor housing when installed in the motor.
These two indexing/mounting bolt receiving apertures also provide a way to index the angular relation between the two rings. When the apertures in each ring align, the upper ring is in its correct operating location relative to the base ring. As stated above, the position of the two rings is maintained by threading an indexing/mounting bolt into the indexing/mounting bolt receiving apertures of the rings. A second locating method calls for the use of a spring loaded detent or spring loaded pin instead of the bolt.
One feature of the present invention is that a rotatable insulator assembly is provided to facilitate the easy replacement of all motor brushes without requiring the dis-assembly or removal of the motor to service the brushes. This feature is accomplished through the use of a two ring configuration briefly explained above and in more depth in the following sections. The base and upper rings are held in place relative to each other with one or more indexing bolts.
Because of its configuration, removing the access door or doors of a typical motor housing usually allows for the easy replacement of at most two brushes. Once the first two brushes have been replaced with the insulator of the present invention, the indexing/mounting bolts are removed and the upper ring rotated 180xc2x0 relative to the base ring.
When the upper ring is so rotated, the final two brushes are positioned adjacent to the opening in the access door and the first two brushes are positioned away from the access door thus permitting the easy replacement of the final two brushes. After the final two brushes are replaced, the upper ring is then rotated back 180xc2x0 relative to the base ring and the indexing/mounting bolts are re-inserted. Depending on the position of the motor and the size of the access panel, it may be necessary to replace the brushes one at a time by incrementally rotating the upper ring by 90xc2x0 three times after removing the first brush.
A second feature of the present invention is that the motor brush holder bolts that are passed through the apertures in the platforms of the upper ring to fasten the brush holder to the upper ring are spring loaded, and biased by the spring axially outwardly to maintain the threaded ends of the bolts in a position axially outwardly, and exteriorly of the axially outwardly facing surface of the platforms on the upper ring, while the head of the bolt is fixedly positioned against rotational movement so that the bolt does not freely rotate about its axis when the nut attached is being tightened or loosened.
These springs bias the bolts axially outwardly toward their threaded ends. The springs are positioned in the axially inner ends of the apertures of the platforms of the upper ring and are disposed between the axially outwardly facing surface of the base ring, and the head of the bolt to urge the head of the bolt axially outwardly away from the base ring. When the bolt is biased axially outwardly to its forward-most position, the spring should still be under some compression to ensure that the bolt will maintain its forward-most, axially outward position.
The enlarged diameter portion of the aperture for receiving the head of the bolt is disposed adjacent to the axially inwardly facing surface of the upper ring, and is not cylindrical in shape but rather slotted, ovaloid or hexagonal. The size of the enlarged portion should be large enough to allow the head of the bolt to pass into and move axially within the aperture, but small enough to engage the flat sides of the head of the bolt to impede the rotation of the head, thereby preventing the bolt from rotating freely in the upper ring.
A third feature of the present invention is that it permits the user to repeatably position the brushes in their proper angular position to maximize brush lifetime. The relative rotational (angular) position of the brushes can impact the operation of the motor and the life expectancy of the brushes. By providing an indexing means, such as the indexing bolt, the user can easily place the brush bracket holding upper ring in the same preferred rotational position after replacing the brushes.
These and other features of the present invention will become apparent to those skilled in the art through a review of the detailed description and figures set forth below, which set forth the best mode of practicing the invention perceived presently by the Applicant.